Atrazine discovery

The share of the herbicide market of individual companies varies with the success that each has found with its discovery programme. Table 1.2 shows the approximate share each major company has of the global herbicide market. The top three companies have launched three very successful compounds that have each managed to establish and maintain a large share of a huge international market - Ciba with atrazine, Monsanto with glyphosate and Zeneca (previously ICI) with paraquat. 

The weed control successes of the triazines led to important discoveries about new and better ways to use herbicides. The remarkable biological success of the triazine herbicides has had a tremendous impact on weed control and crop management over a relatively short time. Sumner (1999) told of his uncle in Hastings, Kansas, who looked over his weed-free com held after he had applied his first atrazine and remarked If I didn t see it with my own eyes, I wouldn t believe it. Such accounts could be repeated many thousands of times in the late 1950s and 1960s. The triazines are still the most important herbicides for weed control in corn, sorghum, and sugarcane. 

Soon after the discovery of triazine-resistant common groundsel, another equally important discovery was made. Radosevich and DeVilliers (1976) found that the mechanism of resistance in this weed was due to insensitive chloro-plasts that were capable of photosynthesis, even in the presence of simazine or atrazine. This was surprising because earlier research had confirmed that there were no differences in plant selectivity or susceptibility due to the origin of chloroplasts. Moreland (1969) had reported that isolated chloroplasts were equally inhibited to simazine whether they came from tolerant com or susceptible spinach. Radosevich and Appleby (1973) had confirmed there were no differences between the susceptible and resistant biotypes of common groundsel due to herbicide uptake, distribution, or metabolism, whereas it is known that com metabolizes triazine herbicides (Shimabukuro, 1985). 

The interactions between y-triazines and microorganisms have been studied over nearly 50 years and new research has led to important discoveries. The isolation of pure cultures that are able to modify or completely mineralize y-triazines has led to the discovery of new genes and enzymes that are involved in the degradation and mineralization of y-triazines by soil bacteria. Studies carried out in soils with a history of repeated y-triazine applications indicate that rapid degradation and mineralization of atrazine developed in various soils (Barriuso and Houot, 1996 Bradley et al, 1997 Pussemier et al, 1997). 

In summary, with the discovery in Dow that a-(2,2,2-trichloroethyl) styrene possessed unique preemergent herbicidal activity and the synthesis and evaluation of close to one thousand related materials, a new product, tridiphane, the active ingredient in TANDEM will enter the marketplace in 1986. Tridiphane will be the first postemergent grass herbicide for use in corn and will be used in combination with triazine herbicides such as atrazine and cyanazine. 

Some synergies appeared fortuitously (atrazine-tridiphane) and not by rational discovery. From what we now know, tridiphane is a metabolic class inhibitor and may have other rational future uses wit herbicides that are detoxified by the same mechanism. 

With regard to substrate-selective sensors with pre-organized cavities, impressive advances have been made in molecular imprinting [55-57]. The discovery of MIP-membrane electro conductivity was an interesting issue, which actually led to the appearance of the earliest MIP sensors [58,59]. It was shown that the membrane electroconductivity could be a function of the interaction between MIP-membrane and ligand (i.e., imprint species) (Fig. 5). An increase in the ligand concentration would result in an enhancement of membrane conductivity. With the same level of concentration, a maximal electro conductivity with the imprint species could be achieved. In addition, it has also been confirmed that polymers imprinted with amino acids, nucleosides, atrazines, sialic acids, or cholesterols can show similar features if coupled with the appropriate transducer [60-64], In particular, molecular imprinting is presently probably the only choice when no suit-... 

The perception of triazines as safe compounds was modified when a chronic study conducted in the mid-1980s showed effects of atrazine on mammary tumors in rats (WHO 1990). As a result, manufacturers introduced restricted personnel exposure levels. The discovery that atrazine was often present where pesticide residues in drinking water exceeded the newly defined European limit of 0.1 /ig/h for any active ingredient, and subsequent media reports and public discussions that made no distinction between detection and hazard, promoted a feeling of insecurity toward the formerly unchallenged products. The development reached a level of misinformation such that atrazine was occasionally chosen as an instrument to attempt suicide (Section III). A virtually unlimited level of tolerance was fortunately experienced in these unfortunate attempts. 

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